30 Comments

Karen Wylie
on April 29, 2020 at 11:07 am

Hello team, congratulations for making it to the final competition! I would like to know more about the following:

-How will you ensure the safety of fish and other aquatic animals near the intake of your solution?
-What purpose does the decanter serve?
-How is the system installed an anchored?
-What happens to your solution during a major flooding event?

The decanter is a critical component of our solution as it provides filtering capabilities. Corkscrew decanters are common industrial equipment that are used for separating solids from liquids and they are a well tested and proven technology. Without this filter, our solution would be unable to remove sediment from the incoming river water.

First among these is installing the pipeline through the dam; this will be done by draining the dam front, and then using a sonic drilling method to drill through the embankment and prevent fracturing.
Here, concrete bases (1 square meter in size, 0.5 m thickness) with pieces of steel rebar (lengths vary) topped with further concrete (~0.2 m in size, 0.1 m thickness) will be attached to the base of the pipeline segments, anchoring our system. This also allows us to build each pipeline according the the respective slope of the sediment leading to the dam embankment, as shown in our sketches of the design.
The pipeline will be installed via a chain/mechanical hoist, operated by a crane, for this section.

From there, installation up several miles of the river will be less novel, following basic S-lay marine pipeline install principles, and is no longer novel to our project; being a basic method of marine pipeline installation.

Hi Karen,
In regards to your question about flooding, our solution is calibrated to take in sediment according to the needs of each specific reservoir. During a flooding event, the increase in water and sediment flow may cause sediment to be washed past our system and continue into the reservoir. In this event, extra measures may be needed to remove sediment and debris from the reservoir.

Thank you, Carolina. Did your design incorporate a factor of safety with capacity in this regard? Could it accommodate any additional sediment for seasonal variations or could an investor ask for this to be taken into consideration?

Unfortunately, changing the amount of sediment the solution can process would require removing the screw and pipe and replacing it with a different calibration, so this wouldn’t be very easy to incorporate for seasonal changes.

In regards to question about fish and aquatic animal safety. The filter (decanter) that is placed before the intake would fix that problem. The filter is there to make sure that only water and sediment make it through to the screw conveyor and pipeline. This was a problem that we looked at in our risk analysis and though possible for fish or other wildlife to get sucked in, it was deemed a low risk problem. This is because the likelihood of this happening is quite small and the risk would not be very high.

Sorry in reading my last response to you I am afraid I may have been a bit unclear, the filter is in front of the decanter. The decanter is what regulates that only sediment and water make it through to the screw conveyor. Before the decanter however is the filter, which is just a small mesh filter that keeps the fish out of harms way. My apologies.

To answer your follow up question, no the decanter was not in our original design. Our original design was to use a corkscrew like the screw conveyor to dig up sediment at the reservoir bed. After research, stakeholder input, and a bit of testing we realized that this design wouldn’t work in actively filtering sediment so then we turned to the decanter idea, which is widely used in industry today and proven to work.

#1 Can you explain if anything similar to this has been done before or other alternatives considered other than dredging?
#2 Can you explain some more detail around how the intake and how sediment makes its way to the inlet?
#3 I am also curious about ongoing maintenance since this system will be challenging to access?

Chris,
To answer your second question, the intake uses the river’s own flow to into the intakes. This river water is sediment rich as it contains sediment that was eroded from upstream. Without the reservoir downstream, this sediment would flow unimpeded and replace other sediment as it is being eroded. However, with the dam in the way all this sediment collects in the reservoir and is never able to reach the rest of the river. By filtering this sediment out of the water just before it enters the reservoir, we can transport to the dam outlet directly and bypass the reservoir.

Briefly mentioned in our video is the process of dredging. This is the most widely used solution for sediment removal in dams. The next most common is dam flushing. Dam flushing is not always a good option, because the downstream river can’t always handle the powerful flow coming from the man made flood. This causes a lot of damage in the ecosystem, not to mention cost in manual labor when digging the flood canals. Any other solutions that are used would be similar to dredging in that they clean up the reservoir but never deposit the sediment anywhere, therefore depriving the downstream river of that nutrients.

In our research we could not find anything similar to what we are doing. That is not to say that it hasn’t been talked about, but during the research and validation of our prototype we could not find any other indications of an active sediment removal system.

#3 I am also curious about ongoing maintenance since this system will be challenging to access?

Hi Chris,

The methods of maintenance for this system will be predominantly based on existing marine pipeline repair methods.
For breakages in the pipe, repair clamps can be installed onto the pipeline from the water’s surface over the breaking point to ensure consistent flow through the pipeline.
For breaks in the decanter, more technical repair will be required; however, via a diver, the decanter can be recovered from the pipeline, fixed outside the pipe, and reinstalled as needed.

Hello- and well done video and congratulations on making the finals! A few questions:
– do you have an expectation on the size fraction which is the highest value for the fish/aquatic life
– how are you minimizing debris through the screw of clogging the screw
– how to minimize aquatic life going through the screw
-how best to drill through the spillway or are you suggesting an alternate route for the installation
-most run of river dams have continuous sediment deposition until full and then it usually runs over the top once full- would you see this as a continuous screw discharge or annual maintenance

In response to your fifth question, we see this as a permanent installation, to continuously filter sediment from the river, then transporting the sediment to the downstream side of the dam. Sediment will be continuously discharged to be carried to the ecosystems downstream.

Robin,
A design feature we realize we would need after some stakeholder input was a way to prevent large debris from entering our decanter. This was determined to be most effectively dealt with with a simple wire-mesh filter placed at the decanter inlet. The very large scale of our decanters would be capable of handling large sediment and would likely just grind it up but this was deemed unnecessary wear and we wanted to ensure we weren’t damaging wildlife.

In response to your third question, to minimize aquatic life going through the screw would not be a risk we are terribly worried about. The screw conveyor is placed at the beginning of the pipeline, after the decanter filters the sediment. The screw conveyor would then move the sediment down through the pipe. The biggest concern would be fish going through the decanter. Though it is not mentioned in our video due to lack of time we did implement a design change towards the end of the semester. A mesh filter placed directly in front of the decanter as to only let water/sediment through. This filter would make it so fish can travel freely through the river.

Thanks for a great question! Based on some of our research, the size fraction fish (primarily Salmonids) benefit the most from is in the range of 8 mm to 128 mm, about the size of rough gravel. Our system is expected to be able to process debris as large as 5 cm so this is not a concern (these larger debris will be filtered).

– how best to drill through the spillway or are you suggesting an alternate route for the installation
Hi Robin,

The route of installation is into the dam embankment foundations themselves, similar to the dam’s intake itself, such that sediment will be exiting along with outflow water processed in the dam.
The method of drilling through the embankment is sonic drilling; vibration-based drilling that best serves to mitigate the risk of fracturing the embankment per the dam reclamations bureau.

Hi Adam,
In response to your sixth and seventh questions:
The maximum size of sediment that could be processed is theoretically more than 5 cm (extremely large) however according to research done by the US Geological Survey, the sediment found in these rivers is very fine (<5 mm) and would be completely unable to clog our system. The chance for rocks, branches or fish to enter our decanter was a major point of concern for us but after some research and stakeholder input, it was clear that a simple mesh filter could be put in place at the system intake to essentially eliminate this possibility. While the system is not easily disassembled, we see this as a very low risk.

We estimate that the installation process could take anywhere from 1-3 months. 3 months being on the high end, most likely about 2 months. Each dam would be different but the biggest dependencies would be the thickness of the dam itself, the length from the dam to the river inlet, the width of the river inlet and flow rate at river inlet. The thickness of the dam will determine how much time it will take to sonic drill through the dam and install the discharge zone. The length from the dam to the river inlet will determine the amount of piping used. The width and flow rate at the river inlet will determine the amount of decanters used, this is because the decanter has a certain radius of effectiveness that is dependent on the flow rate of the river.

Through labor costs and cost of materials it would amount to about $4.5 million dollars. This hiccup though would show benefits within months not only cost but in environmental benefits.

Hi Adam,
Regarding your first question, all dams are in a state of continuous sediment accumulation. All rivers carry sediments and nutrients downstream, and over time these sediments will build up in reservoirs. Not only does this reduce the capacity of water storage (and therefore the efficiency of power production), but it causes the river downstream of the dam to be deprived of the sediments that would provide fish spawning grounds and contribute to natural erosion patterns. Therefore, all dams require some form of regular maintenance to combat this problem, either dredging or flushing. However, neither of these solve the environmental aspect to the problem.

In response to your second question, our solution to sediment is unique because it reintroduces the collected sediment into the river after it travels through the dam. The sediment is deposited at a location near the power plant water output where the flow rate is greatest so that the sediment can continue downstream.

In response to your fifth question, we settled on a pitch for the screw conveyor of 2/3, up to 1:1, of the diameter of the screw itself. This variance is dependent upon the angle of the screw conveyor placement. As long as the screw remains nearly horizontal,0° to 10°, the pitch will be the same as the diameter, or 0.1m. If the screw is placed at a steeper angle the pitch decreases to 2/3 to operate most effectively. This was determined through research of screw conveyor applications, and specifications, as well as small scale testing of various 3d printed screws. In testing, a variety of screws where printed with constant diameters, but varying pitches. These screws where all run at the same RPM, and where compared to see, which pitches where the best for moving sediment the fastest while still being easy to rotate, and not jam with the addition of excess sediment.

Components such as the amount of industrial decanters, the pitch of the screw conveyor, and the diameter of the pipes would differ from dam to dam. This is because a lot of these components are dependent on the flow rate at the river inlet as well as the average concentration of the sediment in the river.

So our design would be able to be retrofitted into any dam, before installation were to occur though some calculations unique to each dam would have to be done.

Hi team,
Congratulations on making it to the final!
I have a few questions:
1 – Would this system need to be installed during dam construction? Or can dams be retrofitted with this system after dam construction, or even after sediment accumulates?
2 – Is this system limited to a specific type of sediment (is there a limit on the particle size)? Could the particles that cannot be moved by this system still accumulate and need to be removed?
3 – In terms of cost comparisons, how does this system compare to the costs of dredging when you take time into consideration. You mention a high cost of dredging per month – but how often does dredging need to occur?
4 – Is the intent of this device to allow the dam to function as more of a “flow through” system for sediment? Where sediment is allowed to move downstream at a similar rate as if the dam was not there?
Thank you!

In response to your fourth question, this device is indeed intended as a “flow through” for sediment. The purpose is to allow sediment to continue downstream, preventing sedimentation of the reservoir, as well as preventing malnutrition downstream due to the lack of nutrient rich sediment.

Hi Karin,
The system is only partially limited to a specific size of sediment mostly for maintenance reasons. The size of particles that are categorized as sediment are only a few millimeters in size or less and we fully anticipate being able to process objects as big as 5 cm. However, these large debris that could enter the decanter would likely cause unnecessary wear and our primary focus was the transportation of sediment downstream to reduce erosion and provide fish spawning ground. For these reasons we implemented a mesh filter at the system intake to prevent these larger objects from entering the decanter.

1 – Would this system need to be installed during dam construction? Or can dams be retrofitted with this system after dam construction, or even after sediment accumulates?

Hi Karin,

The method of installation for our system allows for retrofitting the design into a preexisting dam, outlined below.
Draining the reservoir and flushing the current dam front of water and sediment front provides a “clean slate” such that we are able to drill into the embankment and remove both existing sediment pile-up and water altogether.
Using a sonic drilling method (per the Dam Reclamations Bureau), allows for a safe method of drilling through an existing embankment with minimal risk of fracturing.
Given these parameters, the pipeline can either be retrofitted or installed into a dam as it is being built.

Hello Karin,
In response to your third question, our solution is a one time cost to cover installation and materials and may require maintenance over time. The cost of dredging varies between $2.50 – $25.00 per cubic meter depending heavily on the depth of the water, the amount of accumulation, the size of the reservoir, and the characteristics of the built up sediments. The frequency that dredging needs to be performed varies due to factors such as the size and flow rate of the river feeding in to the reservoir and the size of the reservoir itself. Dredging must be performed at regular intervals each spanning days-weeks. Our solution is a more sustainable alternative to dredging that is less expensive over time and is unique because it reintroduces the sediment back into the river below the dam.
Thanks for your questions,
Carolina